To produce electric energy using certain known wind turbines, rotary electric machines are used to convert kinetic energy to electric energy. Part of the kinetic energy converted by the rotary electric machine is converted to heat, which must be removed to optimize efficiency of the machine. As the temperature increases, the efficiency of the rotary electric machine decreases.
The electric energy produced is subsequently transformed in phase and frequency in stationary electric machines, which are also cooled to optimize performance.
For this purpose, the wind turbines described in U.S. Pat. No. 7,057,305, U.S. Pat. No. 7,161,260, U.S. Pat. No. 6,676,122, U.S. Pat. No. 7,594,800 and EP Patent No. 2,136,077 comprise air cooling systems. More specifically, EP Patent No. 2,136,077 describes a wind turbine comprising a rotary electric machine; a rotary assembly with a hub; blades fitted to the hub; a nacelle supporting the rotary electric machine; and a forced-air cooling system, which feeds air successively through the hub, the rotary electric machine and the nacelle. In other words, air flows in through a first opening in the hub, and out through a second opening in the rear of the nacelle.
Air cooling systems provide for fairly good performance of rotary electric machines on wind turbines installed in relatively mild or cold climates.
In hot climates, on the other hand, liquid cooling systems are required.
U.S. Pat. No. 7,168,251 B1 describes a wind turbine comprising a closed-circuit, liquid cooling system.
Wind turbines must often be designed and built with a cooling system designed according to the climate of where the wind turbine is installed (i.e., to maximize power and efficiency of the electric machine according to the climate at the installation site).
Designing and building wind turbines according to the climate at the installation site, the scale economies made possible by mass production of the wind turbine component parts are greatly reduced.
In this respect, known cooling systems are not particularly versatile and perform relatively poorly as regards to cooling the electric generator.
To eliminate this drawback, Applicant's Patent Application No. EP 2,354,542 proposes a rotor liquid cooling system with a tubular structure fitted with heat exchangers.
This system is highly effective and versatile, but the heat exchangers increase the weight of the rotor.